The present invention relates to a hydraulic system for a servo steering of a motor vehicle, incorporating:
a main valve means producing the assistance pressure applied to a hydraulic assistance device, and including a pair of parallel fluid circuits between a source of pressurized fluid and a reservoir, each fluid circuit comprising at least two restrictions capable of being modulated by rotor means cooperating with stator means, the junction point of the restrictions of each circuit being connected to a respective chamber of the hydraulic assistance device; PA1 a secondary valve means producing the reaction pressure applied to the steering wheel shaft and including a second pair of parallel fluid circuits between a source of pressurized fluid and a reservoir, each of the fluid circuits comprising at least two restrictions capable of being modulated by rotor means cooperating with stator means, rotor means cooperating with the steering wheel shaft.
Such a hydraulic system is known in the art from U.S. Pat. Nos. 4,594,936 and 4,665,798. However, the distributor disclosed in these documents includes an external variable restriction piloted by an on-board computer in order to modify the reaction pressure applied to the steering wheel shaft as a function of the vehicle speed.
This on-board computer and this additional variable restriction are costly, and a cheaper power steering system having a reaction pressure variable with the speed of the vehicle is highly desirable.